In Cassandra 2.1, you can need to enclose trigger names that use uppercase characters in
single quotation marks. The logic comprising the trigger can be written in any Java (JVM)
language and exists outside the database. The Java class in this example that implements the
trigger is named org.apache.cassandra.triggers and defined in an Apache repository. The trigger defined on a table
fires before a requested DML statement occurs to ensures the atomicity of the transaction.

Place the custom trigger code (JAR) in the triggers directory on every
node. The custom JAR loads at startup. The location of triggers directory depends on the installation:

Cassandra 2.1.1 and later supports lightweight transactions for creating a trigger.
Attempting to create an existing trigger returns an error unless the IF NOT EXISTS option is
used. If the option is used, the statement is a no-op if the table already exists.